This invention relates generally to infrared suppression devices and more generally to methods and apparatus for reducing infrared emission from gas turbines such as those used, for example, in helicopters.
In some helicopters used in hostile environments, gear boxes under helicopter rotors are driven by gas turbine engines. These engines rotate at very high RPM, although the helicopter rotors themselves rotate at low RPM because of their diameter. The tailpipes of the gas turbine engines are exhausted overboard. The tailpipe becomes very hot from this hot exhaust gas and thus provides a very bright infrared signal.
With recent advancements in weapons detection technology, there is growing recognition of the importance of reducing the infrared signature associated with gas turbine engines powering military aircraft and land combat vehicles. Signature reductions reduce the possibility of detection and pursuit by enemy anti-aircraft forces including heat-seeking missiles. At least two known configurations have been used to suppress infrared radiation from gas turbine engines. One of these configurations has a center plug is disposed in an exhaust flow that cooperates to block a line of sight to hot turbine parts of the engine. Another blocks the line of sight by ejecting hot gases from the suppressor at a substantial angle from the axial center line of the engine.
An example of an infrared suppressor is disclosed in U.S. Pat. No. 4,295,332, Steyer et al, which describes the use of splitters that perform a dual function of mixing hot and cool gas flows to reduce gas temperatures and also block line-of-sight infrared radiation. Since the conception of the suppressor disclosed in U.S. Pat. No. 4,295,332, additional developments have made possible even more compact and higher performance suppressor construction arrangements. However, even as suppressor construction arrangements have improved, threats have also improved and engine exhaust gas temperatures have been increasing as requirements for increased power and reduced weight have been imposed.
Moreover, current infrared suppression solutions trade performance, payload capability, and/or range for improved survivability. Applicants believe that all currently fielded rotorcraft infrared suppression systems are static systems. For example, one system described in U.S. Pat. No. 6,253,540 provides infrared suppression using static line of sight blockage and the mixing of exhaust gasses with cooling air via ejector action.